At the training centre, they were taught a lot about internal Kana energy, like how it was formed in the body by seven organs called "Kai centres," which were aligned along the spinal cord.
Atmospheric Kana is just pure energy floating around in no specific direction. It is like electromagnetic waves that don't react to electric and magnetic fields. It only reacts to Kana energy and is attracted to it; hence, it is present in the air in the form of intangible threads.
When they come in contact with ionized Kana energy, like energy manifested by an individual, they attach themselves to it. Kana energy is a part of the dark energy, as defined according to human standards—one of the fundamental elements of the universe.
It is free of any particle, even photons, which are the only particles in electromagnetic waves. Thus, if the photons are removed from radiation of energy equal to or higher than gamma radiation, we get Kana energy of intensity proportional to the energy of the radiation used.
When humans extensively used atomic bombs in the Great War, the atmosphere was full of gamma radiation. Kratians came and used their K-filters to convert the radiation into Kana energy.
Internal Kana energy circulates around the body through a special pathway, much like the lymphatic system, except the material being circulated doesn't gather in a common organ. Instead, it radiates from a common organ called Dantian, which is the main Kana reservoir, and distributes itself around the body. The Kana energy inside them is concentrated to such an extent that it travels around the body in a semi-vapor liquefied state.
They have special nodes at intervals called aura nodes. These regulate the Kana flow around the body. They are blocked at some places by birth so that the Kana energy doesn't enter immature organs and harm them. The aura nodes thus block the whole Kana pathway except for necessary organs. Kana energy needs to be circulated through these blocked pathways in order to manifest an Ikanami or just raw Kana energy outside.